select 
MONTHLY as YM,
sum(g) over (order by monthly) MRP
 from
(
select 
x.monthly,ifnull(sum(a.g),0) g
 from
MRR_DATA x left join
(
select
    MONTHLY,NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR as g
from
    MRR_DATA
) A
on x.MONTHLY=DATE(A.MONTHLY,'+1 months')

group by x.MONTHLY order by x.monthly
) a